Acoustic isolation is a motivator for double glazing in some locations. And the vents are small (6mm by 30cm full open).

Most Victorian era houses have 'air bricks' in various locations (terracotta bricks with a small grid of holes in them) and the houses were pretty leaky.

UK government is moving to remove * cooking on open gas from the building regulations for new homes in a few years (big methane/burning fume generator). Eventually as post above parent says we will move to more rational ways of heating the houses. Piping an inflammable gas to millions of houses has always struck me as a bit strange.